1. Field of the Invention
The present invention relates to a biasing force adjusting apparatus used in an electromagnetically driven reciprocating pump comprising a housing with a cylinder, an electromagnet arranged in the housing and supplied with an AC or DC pulse current so as to cyclically repeat magnetization and demagnetization, a piston slidable in the cylinder, a magnetic member mounted in the pump so as to be attracted by an electromagnetic force generated by the energized electromagnet and to cause the piston to slide in the cylinder in one direction along the axis of the cylinder, and a biasing means for accumulating a biasing force by movement of the piston in one direction caused by magnetization of the electromagnet and for causing the pivot to slide in the cylinder in the other direction along the axis of the cylinder upon demagnetization of the electromagnet, the electromagnetically driven reciprocating pump reciprocating the piston in the cylinder so as to achieve pumping, and the biasing force adjusting apparatus being arranged to adjust the magnitude of the biasing force to a predetermined value and, more particularly, to a biasing force adjusting apparatus comprising a biasing means support member being movable relative to the housing, cooperating with the piston to clamp the biasing means in a direction for causing the biasing means to accumulate the biasing force and a direction for causing the biasing means to discharge the biasing force, and changes the clamping force by the movement thereof, and a support member position adjusting means for adjusting a position of the biasing means support member relative to the housing so that the clamping force is set at the predetermined value, thereby adjusting the magnitude of the biasing force to the predetermined value.
2. Description of the Related Art
The electromagnetically driven reciprocating pump, which has a construction described above and to which the biasing force adjusting apparatus is applied, is very popular as a compressor or a vacuum pump. Japanese Patent Publication (Kokoku) shows conventional electromagnetically driven reciprocating pump and conventional biasing force adjusting apparatus used therein.
In FIG. 1, an electromagnetically driven reciprocating pump 10 which comprises a biasing force adjusting apparatus 12 having the same construction as that of the conventional biasing force adjusting apparatus. As shown in FIG. 1, a housing of electromagnetically driven reciprocating pump 10 comprises first housing member 16 with stepped aperture 14, and second housing member 22 with aperture 20 having the same diameter as that of large-diameter portion 18 of stepped aperture 14 of first housing member 16. Second housing member 22 is fixed to first housing member 16 so as to dispose aperture 20 coaxial with large-diameter portion 18 while aperture 20 is adjacent to large-diameter portion 18 of stepped aperture 14 of first housing member 16.
A small-diameter portion of stepped aperture 14 is constituted as cylinder 24 for a piston. Piston 26 is fitted in cylinder 24 so as to be slidable along the longitudinal axis of cylinder 24. An end of cylinder 24 which is away from large-diameter portion 18 is closed by cylinder head member 28 fixed to first housing member 16. A fluid delivery port (not shown) connected to an ON/OFF valve is formed within the area of a circumferential wall portion of cylinder 24 where the inner end face of piston 26 is moved. A second housing member 22 is opened to the atmosphere. Fluid suction port (not shown) is formed in the piston 26 to open in the inner end face (left end face in FIG. 1) and the outer end face (right end face in FIG. 1) of piston 26. Piston 26 has an ON/OFF valve for controlling a fluid flow through the fluid suction port.
Piston 26 has piston drive rod 30 coaxially extending along the central axis of stepped aperture 14 into aperture 20 of second housing member 22. An extended end portion of piston drive rod 30 is inserted in annular guide sleeve 32, formed in second housing member 22 to be coaxially with the central axis in aperture 20 of second housing member 22. The extended end portion of piston drive rod 30 is movable along this central axis in annular guide sleeve 32.
A biasing means support hole 34 is formed in the extended end portion of piston drive rod 30 so as to be opened at the end face of the extended end portion and coaxially arranged with the central axis. A biasing means is arranged in biasing means support hole 34 to bias piston 26 toward the top dead center. In this embodiment, the biasing means is constituted by compression coil 36, one end of which is in contact with the bottom surface of biasing means support hole 34.
The other end of compression coil spring 36 is supported by biasing force adjusting apparatus 12 mounted on second housing member 22.
Biasing force adjusting apparatus 12 has screw member 38 threadably engaged with second housing member 22 at a position coaxial with the central axis such that screw member 38 is movable relative to second housing member 22 along the central axis. Spring seat 40 which contacts the other end of compression coil spring 36 is pressed on through ball 42 the inner end (left end in FIG. 1) of screw member 38 which extends in an area of aperture 20 of second housing member 22 surrounded by the circumferential wall of guide sleeve 32.
Screw member 38, spring seat 40, and ball 42 constitute a biasing means support member for cooperating with biasing means support hole 34 of piston drive rod 30 of piston 26 to clamp compression coil spring 36. When a screwdriver (not shown) having a tip end of a shape corresponding to slot or cross recess 44 formed on the outer end (left end in FIG. 1) of screw member 38 extending outward from second housing member 22 is engaged with slot or cross recess 44, and is turned in one or the other direction, the biasing means support member is moved relative to second housing member 22 in a direction along the central axis to change the clamping force for coil spring 36 generated by cooperation with piston 26.
Nut 48 is threadably engaged with the outer end of screw member 38 through washer 46. Nut 48 is used to fix a position of screw member 38 relative to second housing member 22 and serves as a support member position adjusting means.
Referring to FIG. 1, piston 26 is biased toward the top dead center in biasing cylinder 24 by a preset load (a beginning load) based on the biasing force accumulated in compression coil spring 36 by biasing force adjusting apparatus 12. Iron core 50 for an electromagnet is fixed on the outer surface of first housing member 16. Coil 54 is wound around iron core 50 to cooperate with iron core 50 to constitute electromagnet 52. Coil 54 is connected to an to constitute electromagnet 52 AC power source (not shown) or a DC pulse source (not shown) so that electromagnet 52 repeats magnetization and demagnetization.
Magnetic member 56 is mounted on piston drive rod 30 of piston 26 such that piston 26 is attracted by electromagnet 52 upon energization of electromagnet 52 while piston 26 is located at the top dead center shown in FIG. 1.
In the conventional electromagnetically driven reciprocating pump having the construction described above, when magnetic member 56 is attracted by energized electromagnet 52, piston 26 is moved to the right (FIG. 1) against the biasing force of compression coil spring 36. A fluid is drawn from a fluid suction port (not shown) through an ON/OFF valve (not shown) into a working chamber formed between piston 26 and cylinder head member 28 in cylinder 24. When electromagnet 52 is deenergized, piston 26 is moved to the left (FIG. 1) toward the top dead center by the biasing force accumulated in compression coil spring 36. It is very important to set a position of the upper dead center of piston 26 in cylinder 24, and to at least collision of the head of piston 26 against a partition wall of the working chamber. When the conventional electromagnetically driven reciprocating pump 10 is used as a compressor, movement of piston 26 causes compression of the fluid in the working chamber. The fluid compressed in the working chamber is exhausted from the working chamber through the fluid delivery port (not shown) and the ON/OFF valve (not shown).
Conventional electromagnetically driven reciprocating pump 10 has a relatively large manufacturing error in performance of a biasing means constituted by, e.g., compression coil spring 36 occurs (a free length and a spring constant value of, e.g., compression coil spring 36). In order not to reflect the manufacturing error onto performance of electromagnetically driven reciprocating pump 10, the above-mentioned biasing force adjusting apparatus 12 is employed. More specifically, in the last stage of assembly of electromagnetically driven reciprocating pump 10, biasing force adjusting apparatus 12 is adjusted such that a preset load (a beginning load) applied from the biasing means (compression coil spring 36) to piston 26 is set to be a predetermined value.
However, biasing force adjustment operation by conventional screw rotational type biasing force adjusting apparatus 12 having screw member 38 and nut 48 as major members is inefficient and is incorrect because that operation is done under the operator's in tuition. That is, since the biasing force values set during biasing force adjustment cannot be directly known, variations in the magnitude of biasing forces set during adjustment are inevitably caused.